This may be a simple question, but I can't seem to find the answer on the forums. I have a Mercury and Royal both with GPS units. The value that I am interested in that the GPS reports back is distance . What I am trying to achieve is that when my plane hits a certain distance from the transmitter (the 2000 feet) that it alerts me (very tight fly zone). My question is as follows, is the distance that it provides a straight line. If you look at the image attached. Is the distance given by the GPS the distance to the flag or the distance to the airplane? The flag is a fixed point and so is the pilot (give or take 6 feet) if there is a different way of doing this I am open to any ideas.